Evaluation of the Geophysical Investigations for Rapid Mapping the Maha Sarakham Rock Salt Formation in the Northeast, Thailand

Background Maha Sarakham Rock Salt Formation has been found in the two basins. It is estimated that the rock salt contains more than 18 million million tones of salt (Suwanich, 1994) while the annual world salt production recorded for 1998 indicates that the salt was used at the amount of ~186 million tones per year (Salt Institute, 2000). Thus the Maha Sarakham Rcck Salt can be considered as one of the important mineral resources for the world. These rich deposits can contribute to our well being.

Problems At low pressure and temperature conditions, the rock salt can behave as viscous fluid that can flow easily. Through time, this fluid property of rock salt can produce complex deformation in subsurface geology. When the Maha Sarakham Rock Salt is buried deeply, it becomes mobilized and may flow upwards to form salt domes, deform into discordant bodies, lubricate and fill in surrounding gaps, and drag adjacent strata.

Problems Subsurface geology correlation based on borehores has been found to be very difficult! Rock salt depth found from a few meters to thousand meters from surface. Saline soil with white granular substances of salt on the ground have been exposed during the summer time or all year round in several places in the two basins. Land loss due to salt affect soil has been increased from 5.6% (1984) to 17% (1999)!

What need to done An increased abundance of saline soil and saline water have been found and documented, a thorough study on subsurface geology is needed prior to exploiting the rock salt and development a plan for land use to stop harmful effects of the rock salt in ecosystem. The rock salt depth needs to be mapped for the entire basins to allow relocation the lands that are suitable for agricultural activities and salt production.

What need to done Apply in expensive and effective techniques (i.e., geophysical investigations) for rapid determination of subsurface geology of the rock salt formation.

Objectives of study Conduct three geophysical experiments including Seismic refraction and reflection Gravity and magnetic Resistivity and electromagnetic

Results and discussions Seismic refraction and reflection experiments Gravity and magnetic experiments Resistivity and electromagnetic experiments

Conclusions Seismic refraction or reflection with a single fold can be used to detect the rock salt. Gravity survey alone fails to detect the rock salt layers because of insufficient in the density between rock salt and claystone.

Conclusions Resistivity and electromagnetic surveys can be used to detect the interface between rock salt and saline water, although the results are not conclusive since the measurable bulk resistivity or conductivity did not seem to correlate with the distinct rock salt and the saline water interface. Further studies are needed to derive a definitive conclusion!

Conclusions No magnetic anomaly can be resolved from the rock salt layer because of low- level contrast in magnetic susceptibility of the rock salt relative to the background. Any question!